Laser enhancements of cold sprayed deposits

ABSTRACT

A process for depositing a powder metal onto a substrate is performed by providing a substrate, depositing at least one layer of powder metal onto a surface of the substrate using a non-oxidizing carrier gas so that the powder metal plastically deforms without melting and bonds to a surface upon impact with the surface, and subjecting the at least one powder metal deposited layer to a treatment to improve density and/or raise a temperature of the at least one powder metal deposited layer. In a preferred embodiment of the present invention, the treatment to improve density and/or raise a temperature of the at least one powder metal deposited layer is a laser treatment.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention relates to a process and an apparatus for applyinglocalized improvements to cold sprayed deposited materials.

(2) Prior Art

Cold gas dynamic spraying or “cold spray” has been recently introducedas a new metallization spray technique to deposit powder metal with orwithout inclusions onto a substrate. A supersonic jet of helium and/ornitrogen is formed by a converging/diverging nozzle and is used toaccelerate the powder particles toward the substrate to produce coldspray deposits or coatings. Deposits adhere to the substrate andpreviously deposited layers through plastic deformation and bonding.U.S. Pat. Nos. 5,302,414 and 6,502,767 illustrate cold gas dynamicspraying techniques.

Despite the existence of cold spray techniques improvements are needed.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide aprocess which improves the density of deposited materials and/or raisethe coating temperature.

It is a further object of the present invention to provide an apparatuswhich improves the density of deposited materials and/or raise thecoating temperature.

The foregoing objects may be attained using the process and apparatus ofthe present invention.

In accordance with the present invention, a process for depositing apowder metal onto a substrate is provided. The process broadly comprisesthe steps of providing a substrate, depositing at least one layer ofpowder metal onto a surface of the substrate using a non-oxidizingcarrier gas so that the powder metal plastically deforms without meltingand bonds to a surface upon impact with the surface, and subjecting theat least one powder metal deposited layer to a treatment to improvedensity and/or raise a temperature of the at least one powder metaldeposited layer. In a preferred embodiment of the present invention, thetreatment to improve density and/or raise a temperature of the at leastone powder metal deposited layer is a laser treatment.

Further in accordance with the present invention, an apparatus fordepositing a powder metal onto a substrate is provided. The apparatusbroadly comprises means for depositing at least one layer of powdermetal onto a surface of the substrate using a non-oxidizing carrier gasso that the powder metal plastically deforms without melting and bondsto a surface upon impact with the surface, and means for subjecting theat least one powder metal deposited layer to a treatment to improvedensity and/or raise a temperature of the at least one powder metaldeposited layer.

Other details of the laser enhancements of cold sprayed deposits of thepresent invention, as well as other objects and means attendant thereto,are set forth in the following detailed description and the accompanyingdrawings wherein like reference numerals depict like elements.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of an apparatus for depositing coldsprayed powder metal materials onto a substrate; and

FIG. 2 is a schematic representation of an alternative embodiment of anapparatus for depositing cold sprayed powder metal materials onto asubstrate.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

The present invention relates to a process and an apparatus for applyinglocalized improvements to cold sprayed deposited materials. Thelocalized improvements may be density improvements and/or raising thetemperature of the deposited material high enough for short durations torecover ductility without significant heat input to the substratematerial or any underlying prior cold sprayed deposits.

The cold spray process for depositing powder metal materials ontosubstrates is advantageous in that it provides sufficient energy toaccelerate particles to high enough velocities such that, upon impact,the particles plastically deform and bond to the surface of thesubstrate or onto a previously deposited layer. The process allows thebuild up of a relative dense coating or structural deposit. Cold spraydoes not metallurgically transform the particles from their solid state.

Referring now to FIG. 1, there is shown a system 8 for depositing apowder metal material onto a substrate. The system 8 includes a spraygun 22 having a converging/diverging nozzle 20 through which the powdermetal material is sprayed onto a surface 24 of a substrate 10. Thesubstrate 10 could be a part or component for an engine or for any otherstructure and may be formed from any suitable metallic material known inthe art. The substrate 10 may be held stationary or may be articulated,rotated, or translated by any suitable means (not shown) known in theart.

In the process of the present invention, the material to be deposited isa powdered metal material. The powdered metal material may be of thesame composition as the substrate 10 is made from or it may be acompatible composition. For example, the powder metal material may be anickel based alloy such as IN 718, IN 625, IN 100, WASPALOY, IN 939, orGATORIZED WASPALOY. The powder metal material may also be anothermetallic material such as a copper based alloy or an aluminum basedalloy. The powdered metal materials that are used to form the deposit onthe surface 24 preferably have a diameter in the range of from about 5.0microns to 50 microns (0.2 mils to 2.0 mils). Smaller particle sizesenable the achievement of higher particle velocities. Below 5 microns indiameter, the particles risk getting swept away from the surface 24 dueto a bow shock layer above the surface 24, i.e. insufficient mass topropel the particle through the bow shock. The narrower the particlesize distribution, the more uniform the particle velocity will be. Thisis because the smaller particles in the spray/plume will hit the slower,larger ones and effectively reduce the velocity of both.

The particles to be deposited may be accelerated to supersonicvelocities using compressed gas, such as a gas selected from the groupconsisting of helium, nitrogen, another inert gas, and mixtures thereof.Helium is a preferred gas because it produces the highest velocity dueto its low molecular weight.

The bonding mechanism employed by the process of the present inventionfor transforming the powdered metal material into a deposit is strictlysolid state, meaning that the particles plastically deform but do notmelt. Any oxide layer that is formed on the particles, or is present onthe surface 24, or is present in a previously deposited layer, is brokenup and fresh metal-to-metal contact is made at very high pressures.

The powdered metal material used to form the deposit may be fed to thespray gun 22 using any suitable means known in the art, such as modifiedthermal spray feeders. One custom designed feeder that may be used ismanufactured by Powder Feed Dynamics of Cleveland, Ohio. This feeder hasan auger type feed mechanism. Fluidized bed feeders and barrel rollfeeders with an angular slit may also be used.

In the process of the present invention, the feeders may be pressurizedwith a gas selected from the group consisting of helium, nitrogen,another inert gas, and mixtures thereof. Feeder pressures are generally15 psi above the main gas or head pressures, which pressures are usuallyin the range of from 200 psi to 500 psi, depending on the powder metalmaterial composition. The main gas is preferably heated so that gastemperatures are in the range of from 600 degrees Fahrenheit to 1200degrees Fahrenheit. If desired, the main gas may be heated as high asapproximately 1250 degrees Fahrenheit depending on the material beingdeposited. The gas may be heated to keep it from rapidly cooling andfreezing once it expands past the throat of nozzle 20. The net effect isa surface temperature on the substrate 10 of about 115 degreesFahrenheit during deposition. Any suitable means known in the art may beused to heat the gas.

To deposit the powdered metal material, the nozzle 20 may pass over thesurface 24 of the substrate 10 being repaired on multiple occasions. Thenumber of passes is a function of the thickness of the material to beapplied. The process of the present invention is capable of forming adeposit having any desired thickness. Cold spray can produce thin layersranging from 0.002 inches to 0.020 inches per single pass.

The main gas that is used to deposit the powdered metal particles ontothe surface 24 may be passed through the nozzle 20 via inlet 30 at aflow rate of from 0.001 SCFM to 50 SCFM, preferably in the range of from15 SCFM to 35 SCFM. The foregoing flow rates are preferred if helium isused as the main gas. If nitrogen is used by itself or in combinationwith helium as the main gas, the nitrogen may be passed through thenozzle 20 at a flow rate of from 0.001 SCFM to 30 SCFM, preferably from4.0 SCFM to 30 SCFM.

The main gas temperature may be in the range of from 600 degreesFahrenheit to 1200 degrees Fahrenheit, preferably from 700 degreesFahrenheit to 1000 degrees Fahrenheit, and most preferably from 725degrees Fahrenheit to 900 degrees Fahrenheit.

The pressure of the spray gun 22 may be in the range of from 200 psi to500 psi, preferably from 200 psi to 400 psi, and most preferably from275 psi to 375 psi. The powdered metal material is preferably fed from ahopper, which is under a pressure of 10 to 50 psi higher than thespecific main gas pressure, preferably 15 psi higher, to the spray gun22 via line 34 at a rate in the range of from 10 grams/min to 100grams/min, preferably from 15 grams/min to 50 grams/min.

The powdered metal material is fed to the spray gun 22 using anon-oxidizing carrier gas. The carrier gas may be introduced via inlet30 at a flow rate of from 0.001 SCFM to 50 SCFM, preferably from 8.0SCFM to 15 SCFM. The foregoing flow rate is useful if helium is used asthe carrier gas. If nitrogen by itself or mixed with helium is used asthe carrier gas, a flow rate of from 0.001 SCFM to 30 SCFM, preferablyfrom 4.0 to 10 SCFM, may be used.

The spray nozzle 20 is held at a distance from the surface 24. Thisdistance is known as the spray distance and may be in the range of from10 mm. to 50 mm.

The velocity of the powdered metal particles leaving the spray nozzle 20may be in the range of from 825 m/s to 1400 m/s, preferably from 850 m/sto 1200 m/s.

As mentioned before, the powdered metal material may be deposited ontothe surface 24 so as to form a coating having one or more layers. It hasbeen discovered that the deposited layer(s) could receive localizedimprovements from laser processing. With proper settings, a laser couldbe passed directly over a deposited layer to improve density (sintering)and/or raise the coating temperature high enough, for a short duration,to recover ductility without significant heat input to the substratematerial or underlying prior cold sprayed layer (small thermalgradient). To this end, the system 8 includes a laser 60 which may bemovable to allow the laser beam to apply heat to the entire powder metalmaterial deposit. The laser 60 may comprise any suitable laser known inthe art such as a YAG laser. The laser processing may be performed aftereach successive cold sprayed layer deposit.

As shown in FIG. 2, the laser 60 may be mounted to the nozzle 20 ifdesired so that the laser 60 moves with the nozzle 20. Such a laserwould track along the spray beam while locally enhancing the deposit (insitu heat treatment).

Cold spray coatings are highly cold worked due to the extreme impactvelocity and the nature of the bonding mechanism. This degree of coldwork results in very low tensile ductility of the deposited material.Also, some high hardness materials produce fairly porous deposits evenat the highest possible spray parameters. The use of the laser 60 helpsimprove the ductility of the deposited material. It can also increasethe density or reduce the porosity of deposited material.

The cold spray process offers many advantages over other metallizationprocesses. Since the powders are not heated to high temperatures, nooxidation, decomposition, or other degradation of the feedstockmaterials occurs. Powder oxidation during deposition is also controlledsince the particles are contained within the oxygen-free acceleratinggas stream. Other potential advantages include the formation ofcompressive residual surface stresses and retaining the microstructureof the feedstock. Also, because relatively low temperatures are used,thermal distortion of the substrate will be minimized. Because thefeedstock is not melted, cold spray offers the ability to depositmaterials that cannot be sprayed conventionally due to the formation ofbrittle intermetallics or a propensity to crack upon cooling or duringsubsequent heat treatments.

It is apparent that there has been provided in accordance with thepresent invention laser enhancements of cold sprayed deposits whichfully satisfy the objects, means, and advantages set forth hereinbefore.While the present invention has been described in the context ofspecific embodiments thereof, other alternatives, modifications, andvariations will become apparent to those skilled in the art having readthe foregoing description. Therefore, it is intended to embrace thosealternatives, modifications, and variations which fall within the broadscope of the appended claims.

1. A process for depositing a powder metal onto a substrate comprisingthe steps of: providing a substrate; depositing at least one layer ofpowder metal onto a surface of said substrate using a non-oxidizingcarrier gas so that said powder metal plastically deforms withoutmelting and bonds to a surface upon impact with said surface; andsubjecting said at least one powder metal deposited layer to a treatmentto improve density and/or raise a temperature of said at least onepowder metal deposited layer.
 2. The process according to claim 1,wherein said subjecting step comprises utilizing a laser to improve saiddensity and/or raise said temperature.
 3. The process according to claim1, wherein said depositing step comprises depositing multiple layers ofsaid powder metal.
 4. The process according to claim 3, wherein saidsubjecting step is performed after each said layer is deposited.
 5. Theprocess according to claim 4, wherein each said subjecting stepcomprises utilizing a laser to improve said density and/or raise saidtemperature.
 6. The process according to claim 1, wherein saiddepositing step comprises depositing multiple layers of said powdermetal and said subjecting step is performed after said multiple layershave been deposited.
 7. The process according to claim 1, wherein saiddepositing step comprises providing said powder metal in particle formhaving a particle size in the range of from 5 microns to 50 microns andaccelerating said particles to a speed in the range of from 825 m/s to1400 m/s.
 8. The process according to claim 7, wherein said acceleratingstep comprises accelerating said particles to a speed in the range offrom 850 m/s to 1200 m/s.
 9. The process according to claim 7, whereinsaid depositing step further comprises feeding said powder metal to aspray nozzle at a feed rate of from 10 grams/min to 100 grams/min usinga carrier gas selected from the group consisting of helium, nitrogen,another inert gas, and mixtures thereof.
 10. The process according toclaim 9, wherein said feeding step comprises feeding said metal powderto said spray nozzle at a feed rate of from 15 grams/min to 50grams/min.
 11. The process according to claim 9, wherein said carriergas is helium and said feeding step comprises feeding helium to saidnozzle at a flow rate of from 0.001 SCFM to 50 SCFM.
 12. The processaccording to claim 11, wherein said feeding step comprises feeding saidhelium to said nozzle at a flow rate in the range of from 8.0 SCFM to 15SCFM.
 13. The process according to claim 9, wherein said carrier gascomprises nitrogen and said feeding step comprises feeding said nitrogento said nozzle at a flow rate of from 0.001 SCFM to 30 SCFM.
 14. Theprocess according to claim 13, wherein said feeding step comprisesfeeding said nitrogen to said nozzle at a flow rate of from 4.0 SCFM to10 SCFM.
 15. The process according to claim 7, wherein said depositingstep comprises passing said metal powder particles through said nozzleusing a main gas selected from the group consisting of helium, nitrogen,another inert gas, and mixtures thereof at a main gas temperature in therange of from 600 degrees Fahrenheit to 1200 degrees Fahrenheit and at aspray pressure in the range of from 200 psi to 500 psi.
 16. The processaccording to claim 15, wherein said passing step comprising passing saidmetal powder particles through said nozzle at a main gas temperature inthe range of from 700 degrees Fahrenheit to 1000 degrees Fahrenheit at aspray pressure in the range of from 200 psi to 400 psi.
 17. The processaccording to claim 15, wherein said main gas temperature is in the rangeof from 725 degrees Fahrenheit to 900 degrees Fahrenheit at a spraypressure in the range of from 275 psi to 375 psi.
 18. The processaccording to claim 15, wherein said main gas comprises helium and saidpassing step comprises feeding said helium to said nozzle at a flow ratein the range of from 0.001 SCFM to 50 SCFM.
 19. The process according toclaim 18, wherein said helium feeding step comprises feeding said heliumto said nozzle at a flow rate in the range of from 15 SCFM to 35 SCFM.20. The process according to claim 15, wherein said main gas comprisesnitrogen and said passing step comprises feeding said nitrogen to saidnozzle at a feed rate in the range of from 0.001 SCFM to 30 SCFM. 21.The process according to claim 20, wherein said nitrogen feeding stepcomprises feeding said nitrogen to said nozzle at a feed rate in therange of from 4.0 to 8.0 SCFM.
 22. The process according to claim 1,wherein said depositing step comprises depositing each layer at athickness of from 0.002 inches to 0.020 inches.
 23. An apparatus fordepositing a powder metal onto a substrate comprising: means fordepositing at least one layer of powder metal onto a surface of saidsubstrate using a non-oxidizing carrier gas so that said powder metalplastically deforms without melting and bonds to a surface upon impactwith said surface; and means for subjecting said at least one powdermetal deposited layer to a treatment to improve density and/or raise atemperature of said at least one powder metal deposited layer.
 24. Anapparatus according to claim 23, wherein said subjecting means comprisesa laser.
 25. An apparatus according to claim 23, wherein said depositingmeans comprises: a source of powder metal; and means for delivering saidpowder metal to a convergent-divergent spray nozzle so that said powdermetal exits said nozzle at a speed of from 825 m/s to 1400 m/s.
 26. Anapparatus according to claim 25, wherein said delivering means comprisesmeans for supplying a carrier gas selected from the group consisting ofhelium, nitrogen, another inert gas, and mixtures thereof.
 27. Anapparatus according to claim 25, wherein said subjecting means comprisesa laser attached to said spray nozzle.